The major question to be addressed by this study is: "What is the association between semen abnormalities in an adult male population seeking treatment for subferility and exposures to environmental agents, including those resulting from occupation and other risk factors associated with personal behavior (including the use of: alcohol, cigarettes, drugs, hot baths and materials related to hobbies)?" To answer this question, a case control study will be conducted among patients seeking treatment at the Yale-New Haven Hospital Infertility Clinic. The male partners of all couples entering the Infertility Clinic over a three year period will be invited to participate in the study. Detailed information will be ascertained from each man concerning: 1) medical history, 2) medical therapies, 3) family genetic history; 4) reproductive history, 5) occupational history, 6) military service, 7) recreational activities, and 8) personal habits, prior to his classification as a case or control. In addition, each man will be physically examined by a physician specializing in infertility and diagnostic laboratory tests, including at least two semen analyses, will be performed. Based on the results of the semen analyses, men with semen abnormalities will be designated as the cases and the remaining group of men will be the controls. The major parameters for determining semen quality include: density, mortality, and morphology. The data collected from the study participants will be analyzed to identify the variables which best differentiate the cases from the controls, based upon the various elements of their histories. In addition, the magnitude of risk for having abnormal semen in relation to each environmental exposure will be computed using the Odds Ratio. These risk estimates will be computed for specific types of semen abnormality, for groups of these abnormalities, and for all of them combined. Determination, within the data set, of confounding and effect modifying factors will be made and controlled for appropriately by using log linear models. The final analysis will also include multivariable analysis to evaluate risk factor interaction. The project is planned for a four year period. During the 36 months of subject recruitment, we expect to enroll 593 cases and 89 controls.